and essential constituent of alkaline nature, the term oxygen or acidifier; his new discovery of the simplicity of oxymuriatic acid, showed the theoretical system of chemical language to be equally vicious in another respect. Hence this philosopher most judiciously discarded the appellation oxymuriatic acid, and introduced in its place the name chlorine, which merely indicates an obvious and permanent character of the substance, its greenish yellow colour. The more recent investigations of chemists on fluoric, hydriodic, and hydrocyanic acids have brought powerful analogies in support of the chloridic theory, by showing that hydrogen alone can convert certain undecompounded bases into acids well characterized, without the aid of oxygen. Dr. Murray indeed has endeavoured to revive and new-model the early opinion of Sir H. Davy, concerning the necessity of the presence of water, its elements, to the constitution of acids. He conceives that many acids are ternary compounds of a radical with oxygen and hydrogen; but that the two latter ingre dients do not necessarily exist in them in the state of water. Oil of vitriol, for instance, in this view, instead of consisting of 81. 5 real acid, and 18.5 water in 100 parts may be regarded as a compound of 32.6 sulphur + 65.2 oxygen + 2.2 hydrogen. When it is saturated with an alkaline base, and exposed to heat, the hydrogen unites to its equivalent quantity of oxygen, to form water, which evaporates, and the remaining oxygen and the sulphur or combine with the base. But when the acid is made to act on a metal, the oxygen partly unites to it, and hydrogen alone escapes. "Nitric acid, in its highest state of con centration, is not a definite compound of real acid, with about a fourth of its weight of water, but a tenary compound of nitrogen, oxygen, and hydrogen. Phosphoric acid is a triple compound of phosphorus, oxygen, and hydrogen; and phospho. rous acid is the proper binary compound of phosphorus and oxygen. The oxalic, tartaric, and other vegetable acids, are ad mitted to be ternary compounds of carbon, oxygen, and hydrogen; and are therefore in strict conformity to the doctrine now illustrated. "A relation of the elements of bodies to acidity is thus discovered different from what has hitherto been proposed. When a series of compounds exists, which have certain common characteristic properties, and when these compounds all contain a common element, we conclude, with justice, that these properties are derived more peculiarly from the action of this element. On this ground Lavoisier inferred, by an ample induction, that oxygen is a principle of acidity. Berthollet brought into view the conclusion, that it is not exclusively so, from the examples of prussic acid and sulphuretted hydrogen. In the latter, acidity appeared to be produced by the action of hydrogen. The discovery by Gay-Lussac, of the compound radical cyanogen, and its conversion into prussic acid by the addition of hydrogen, confirmed this conclusion; and the discovery of the relations of iodine still further established it. And now, if the preceding views are just, the system must be still further modified. While each of these conclusions are just to a certain extent, each of them requires to be limited in some of the cases to which they are applied; and while acidity is sometimes exclusively connected with oxygen, sometimes with hydrogen, the principle must also be admitted, that it is more frequently the result of their combined operation. "There appears even sufficient reason to infer, that, from the united action of these elements, a higher degree of acidity is acquired than from the action of either alone. Sulphur affords a striking example of this. With hydrogen it forms a weak acid. With oxygen it also forms an acid, which, though of superior energy, still does not display much power. With hydrogen and oxygen it seems to receive the acidifying influence of both, and its acidity is proportionally exalted. "Nitrogen, with hydrogen, forms a compound altogether destitute of acidity, and possessed even of qualities the reverse.With oxygen, in two definitive proportions, it forms oxides; and it is doubtful if, in any proportion, it can establish with oxygen an insulated acid. But with oxy gen and hydrogen in union it forms nitric acid, a compound more permanent, and of energetic action." It is needless to give at more detail Dr. Murray's speculations, which, supposing them plausible in a theoretical point of view, seem barren in practice; at least their practical tendency cannot be perceived by the editor of this work. It is sufficiently singular, that, in an attempt to avoid the mysterious and violent transformations, which, on the chloridic theory, a little moisture operates on common salt, instantly changing it from chlorine and sodium, into muriatic acid and soda, Dr. Murray should have actually multiplied, with one hand, the very difficulties which he had laboured, with the other, to re move. He thinks it doubtful if nitrogen and oxygen can alone form an insulated acid.Hydrogen he conceives essential to its energetic action. What, we may ask then, exists in dry nitre, which contains no hy drogen? Is it nitric acid, or merely two of its elements, in want of a little water to furnish the requisite hydrogen? The same questions may be asked relative to the sul the carbonic, or rank higher in the scale of acidity, then, on adding to a given weight of liquid muriate of lime, a mixture of oxalate and carbonate of ammonia, phate of potash. Since he conceives hy- each in equivalent quantity to the drogen necessary to communicate full force to sulphuric and nitric acids, the moment they lose their water they should lose their saturating power, and become incapable of retaining caustic potash in a neutral state. Out of this dilemma he may indeed try to escape, by saying, that moisture or hydrogen is equally essential to alkaline strength, and that therefore the same desiccation or de-hydrogenation which impairs the acid power, impairs also that of its alkaline antagonist. The result must evidently be, that, in a saline hydrate or solution, we have the reciprocal attractions of a strong acid and alkali, while, in a dry salt, the attractive forces are those of relatively feeble bodies. On this hypothesis, the difference ought to be great between dry and moistened sulphate of potash. Carbonic acid he admits to be destitute of hydrogen; yet its saturating power is very conspicuous in neutralizing dry lime. Now, oxalic acid, by the last analysis of Berzelius, contains no hydrogen. It differs from the carbonic only in the proportion of its two constituents. And oxalic acid is appealed to by Dr. Murray as a proof of the superior acidity bestowed by hydrogen. On what grounds he decides carbonic to be a feebler acid than oxalic, it is difficult to see. By Berthollet's test of acidity, the former is more energetic than the latter in the proportion of 100 to about 58; for these numbers are inversely as the quantity of each requisite to saturate a given base. If he be inclined to reject this rule, and appeal to the decomposition of the carbonates by oxalic acid, as a criterion of relative acid power, let us adduce his own commentary on the statical affinities of Berthollet, where he ascribes such changes not to a superior attraction in the decomposing substance, but to the elastic tendency of that which is evolved. Ammonia separates magnesia from its muriatic solution at common temperatures; at the boiling heat of water, magnesia separates ammonia. Carbonate of ammonia, at temperatures under 230°, precipitates carbonate of lime from the muriate; at high er temperatures the inverse decomposition takes place with the same ingredients. If the oxalic be a more energetic acid than reous salt, oxalate of lime ought alone to be separated. It will be found, on the contrary, by the test of acetic acid, that as much carbonate of lime will precipitate as is sufficient to unsettle these speculations. Finally, dry nitre, and dry sulphate of potash, are placed, by this supposition, in as mysterious a predicament as dry muriate of soda in the chloridic theory. Deprived of hydrogen, their acid and alkali are enfeebled or totally changed. With a little water both instantly recruit their powers. In a word, the solid sulphuric acid of Nordhausen, and the dry potash of potassium, are alone sufficient to subvert this whole hypothesis of hydrogenation. We shall introduce, under the head of alkali, some analogous speculations by Dr. Murray on the influence of the elements of water on that class of bodies. Edin. Phil. Trans. vol. viii. part 2d.† After these observations on the nature of acidity, we shall now state the general properties of the acids. 1. The taste of these bodies is for the most part sour, as their name denotes; and in the stronger species it is acrid and corrosive. 2. They generally combine with water in every proportion, with a condensation of volume and evolution of heat. 3. With a few exceptions they are volatilized or decomposed at a moderate heat. 4. They usually change the purple colours of vegetables to a bright red. 5. They unite in definite proportions † I conceive Mr. Murray's views on this subject as nearer the truth than those of the editor. I had adopted conclusions somewhat similar, ere I met with them. As the characteristic attributes of acidity are never observed in the absence of moisture, water would seem to have higher pretensions to be considered as the acidifying principle than any other ponderable substance. It may be a question, whether acids in a very high state of dephlegmation are really acids or act as such. They do not merely change vegetable blues; they destroy them. They do not produce a sour taste upon the tongue, they cauterize it, and are destructive of, or are destroyed by, substances, which, in a weaker state, they would combine with, so as to yield them up uninjured in obedience to higher affinities. Concentrated sulphuric acid destroys organic products, by taking up the elements with the alkalis, earths, and metallic oxides, and form the important class of salts. This may be reckoned their characteristic and indispensable property. The powers of the different acids were originally estimated by their relative causticity and sourness, afterwards by the scale of their attractive force towards any particular base, and next by the quantity of the base which they could respectively neutralize. But Berthollet proposed the converse of this last criterion as the measure of their powers. "The power with which they can exercise their acidity," he estimates "by the quantity of each of the acids which is required to produce the same effect, viz. to saturate a given quantity of the same alkali." It is therefore the capacity for saturation of each acid, which, in ascertaining its acidity, according to him, gives the comparative force of the affinity to which it is owing. Hence he infers, that the affinity of the different acids for an alkaline base, is in the inverse ratio of the ponderable quantity of each of them which is necessary to neutralize an equal quantity of the same alkaline base. An acid is, therefore in this view, the more powerful, when an equal weight can saturate a greater quantity of an alkali. Hence, all those substances which can saturate the alkalis, and cause their properties to disappear, ought to be classed among the acids; in like manner, among the alkalis should be placed all those which, by their union, can saturate acidity. And the capacity for saturation being the measure of this property, it should be employed to form a scale of the comparative power of alkalis as well as that of acids. However plausible, a priori, the opinion of water and leaving the carbon. Hence its blackening power. When diluted, it acts in a totally different way. Of course if it be an acid in the last case, it cannot be so in the first. In evolving carbon by its action on alcohol, it is precisely analogous to potash, which darkens that fluid, and evolves a carbonaceous resin, which may be seen when the alcoholic solution of that alkali is evaporated, in order to obtain the hydrate. It seems to me that the galvanic fluid is the acidifying principle, and that the acid state is the consequence of galvanic arrangements or polarities. It is known that moisture is indispensable to the efficiency of these. On adding water to concentrated sulphuric acid, the hydrogen and oxygen severally go to the different poles of the previous compound. Hence the hydrogen evolved by iron or zinc and diluted sulphuric acid, does not come from a simultaneous, but a previous decomposition of water. of their quantities, viz. and -; yet 36 52 the very opposite effect takes place, for lime separates magnesia from nitric acid. And, in the present example, the difference of effect cannot be imputed to the difference of force with which the substances tend to assume the solid state. We have therefore at present no single acidifying principle, nor absolute criterion of the scale of power among the different acids: nor is the want of this of great importance. Experiment furnishes us with the order of decomposition of one acidoalkaline compound by another acid, whether alone, or aided by temperature; and this is all which practical chemistry seems to require. Before entering on the particular acids we shall here describe the general process by which M. Thenard has lately succeeded in communicating to many of them apparently a surcharge of oxygen, and thus producing a new class of bodies, the oxygenized acids, which he has had the good fortune of forming and making known to the chemical world. The first notice of these new compounds appeared in the Ann. de Chimie et Physique, viii. 306. for July 1818, since which time several additional communications of a very interesting nature have been made by the same celebrated chemist. He has likewise formed a compound of water with oxygen, in which the proportion of the latter principle is doubled, or 616 times its volume is added. The methods of oxygenizing the liquid acids and water, agree in this, that deutoxide of barium is formed first of all, from which the above liquids, by a subsequent process, derive their oxygen. He prescribes the following precautions, without which success will be only partial. 1. Nitrate of barytes should first be obtained perfectly pure, and, above all, free from iron and manganese. The most certain means of procuring it, is to dissolve the nitrate in water, to add to the solution a small excess of barytes water, to filter and crystallize. 2. The pure nitrate is to be decomposed by heat. This ought not to be done in a common earthenware retort, because it contains too much of the oxides of iron and manganese, but in a perfectly white porcelain retort. Four or five pounds of nitrate of barytes may be decomposed at once, and the process will require about three hours. The barytes thus procured will contain a considerable quantity of silex and alumina; but it will have only very minute traces of manganese and iron, a circumstance of essential importance. 3. The barytes, divided by a knife into pieces as large as the end of the thumb, should then be placed in a luted tube of glass. This tube should be long and large enough to contain from 24 to 34 libs. It is to be surrounded with fire, and heated to dull redness, and then a current of dry oxygen gas is to be passed through it. However rapid the current, the gas is completely absorbed; so that when it passes by the small tube, which ought to terminate the larger one, it may be concluded that the deutoxide of barium is completed. It is, however, right to continue the current for seven or eight minutes more. Then the tube being nearly cold, the deutoxide, which is of a light grey colour, is taken out, and preserved in in stoppered bottles. When this is moistened it falls to powder, without much increase of temperature. If in this state it be mixed with seven or eight times its weight of water, and a dilute acid be poured in, it dissolves gradually by agitation, without the evolution of any gas. The solution is neutral, or has no action on turnsole or turmeric. When we add to this solution the requisite quantity of sulphuric acid, a copious precipitate of barytes falls, and the filtered liquor is merely water, holding in solution the oxygenized acid, or deutoxide of hydrogen, combined with the acid itself. The class of acids has been distributed into three orders, according as they are derived from the mineral, the vegetable, or the animal kingdom. But a more specific distribution is now requisite. They have also been arranged into those which have a single, and those which have a compound basis or radical. But this arrangement is not only vague, but liable in other respects to considerable objections. The chief advantage of a classification is to give general views to beginners in the study, by grouping together such substances as have analogous properties or composition. These objects, it is hoped, will be tolerably well attained by the following divisions and subdivisions. Division 1st. Acids from inorganic nature, or which are procurable without having recourse to animal or vegetable products. Division 2d. Acids elaborated by means of organization. The first group is subdivided into three families, 1st, Oxygen acids; 2d, Hydrogen acids; 3d, Acids destitute of both these supposed acidifiers. 35. Succinic. 36. Sulphovinic! 37. Tartaric. 38. Zumic. 19. Menispermic. The acids of the last division are all decomposable at a red heat, and afford generally carbon, hydrogen, oxygen, and in some few cases also nitrogen. The mellitic is found like amber in wood coal, and like it, is undoubtedly of organic origin. We shall treat of them all in alphabetical order, only joining those acids together which graduate, so to speak, into each other, as hyposulphurous, sulphurous and sulphuric.* * ACID (ACERIC). A peculiar acid said to exist in the juice of the maple. It is decomposed by heat, like the other vegetable acids.* * ACID (ACETIC). The same acid which, in a very dilute and somewhat impure state, is called vinegar. : This acid is found combined with potash in the juices of a great many plants; particularly the sambucus nigra, phœnix dactilifera, galium verum, and rhus typhinus. Sweat, urine, and even fresh milk contain it. It is frequently generated in the stomachs of dyspeptic patients. Almost all dry vegetable substances, and some animal, subjected in close vessels to a red heat, yield it copiously. it is the result likewise of a spontaneous fermentation, to which liquid vegetable, and animal matters are liable. Strong acids, as the sulphuric and nitric, develope the acetic by their action on vegetables. It was long supposed, on the authority of Boerhaave, that the fermentation which forms vinegar is uniformly preceded by the vinous. This is a mistake. Cabbages sour in water, making sour crout; starch in starch-makers' sour waters; and dough itself, without any previous production of wine. The varieties of acetic acids known in commerce are four: 1st, Wine vinegar; 2d, Malt vinegar; 3d, Sugar vinegar; 4th, Wood vinegar. We shall describe first the mode of making these commercial artieles, and then that of extracting the absolute acetic acid of the chemist, either from these vinegars, or directly from chemical compounds, of which it is a constituent. The following is the plan of making vinegar at present practised in Paris. The wine destined for vinegaris mixed in a large tun with a quantity of wine lees, and the whole being transferred into cloth-sacks, praced placed within a large iron-bound vat, the liquid matter is extruded through the sacks by superincumbent pressure. What passes through is put into large casks, set upright, having a small aperture in their top. In these it is exposed to the heat of the sun in summer, or to that of a stove in winter. Fermentation supervenes in a few days. If the heat should then rise too high it is lowered by cool air, and the addition of fresh wine. In the skilful regulation of the fermentative temperature consists the art of making good wine vinegar. In summer the process is generally completed in a fortnight; in winter double the time is requisite. The vinegar is then run off into barrels, which contain several chips of birch-wood. In about a fortnight it is found to be clarified, and is then fit for the market. It must be kept in close casks. The manufacturers at Orleans prefer wine of a year old for making vinegar. But if by age the wine has lost its extractive matter, it does not readily undergo the acetous fermentation. In this case, acetification, as the French term the process, may be determined by adding slips of vines, bunches of grapes or green woods. It has been asserted that alcohol, added to fermentable liquor, does not increase the product of vinegar.But this is a mistake. Stahl observed long ago, that if we moisten roses, or lilies with alcohol, and place them in vessels in which they are stirred from time to time, vinegar will be formed. He also informs us, if after abstracting the citric acid from lemon juice by crabs' eyes (carbonate of lime), we add a little alcohol to the supernatent liquid, and place the mixture in a proper temperature, vinegar will be formed. Chaptal says, that two pounds of weak spirits, sp. gr, 0.985, mixed with 300 grains of beer yeast, and a little starch water, produced extremely strong vinegar. The acid was developed on the 5th day. The same quantity of starch and yeast, without the spirit, fermented more slowly, and yielded a weaker vinegar. A slight motion is found to favour the formation of vinegar, and to endanger its decomposition after it is made. Chaptal ascribes to agitation the operation of thunder; though it is well known, that when the atmosphere is highly electrified, beer is apt to become suddenly sour, without the concussion of a thunder-storm. In cellars exposed to the vibrations occasioned by the rattling of carriages, vinegar does not keep well. The lees, which had been deposited by means of isinglass and repose, are thus jumbled into the liquor, and make the fermentation recommence. Almost all the vinegar of the north of France being prepared at Orleans, the manufactory of that place has acquired such celebrity, as to render their process worthy of a separate consideration. The Orleans' casks contain nearly 400 pints of wine. Those which have been already used are preferred. They are placed in three rows, one over another, and in the top have an aperture of two inches diameter, kept always open. The wine for acetification is kept in adjoining casks,containing beech shavings, to which the lees adhere. The wine thus clarified is drawn off to make vinegar. One hundred pints of good vinegar, boiling hot, are first poured into each cask, and left there for eight days. Ten pints of wine are mixed in, every eight days, till the vessels are full. The vinegar is allowed to remain in this state fifteen days, before it is exposed to sale. The used casks, called mothers, are never emptied more than half, but are successively filled again, to acetify new portions of wine. In order to judge if the mother works, the vinegar makers plunge a spatula into the liquid; and according to the quantity of froth which the spatula shows, they add more or less wine. In summer, the atmospheric heat is sufficient. In winter, stoves heated to about 75° Fahr. maintain the requisite temperature in the manufactory. In some country districts, the people keep in a place, where the temperature is mild and equable, a vinegar cask, into |